Previous work from our laboratories has shown that the time required for the upstroke of the action potential to regain its steady state characteristics becomes progressively longer as the resting membrane potential decreases. The antiarrhythmic drug lidocaine also prolongs these recovery kinetics. The profound work is designed to assess 1) the affects of hypoxia and ischemia on these parameters in order to gain further insight into the causes of slowed conduction 2) the affects of other antiarrhythmic drugs, in order to characterize their actions more precisely than is possible from existing studies and 3) the kinetic characteristics of conductive velocity in intact hearts following the introduction of premature beats, increase in rate, partial depolarization (produced by increasing extracellular K ion) and the administration of antiarrhythmic drugs in order to evaluate the applicability of data derived from single fiber studies to the intact heart and to gain a greater understanding of the facts responsible for alterations in conduction velocity and therefore, arrhythmia production. DTX* 1HE-13237-5*